Perpendicular recording has been developed in part to achieve higher recording density than is realized with longitudinal recording devices. A PMR write head typically has a main pole layer with a small surface area at an ABS, and coils that conduct a current and generate a magnetic flux in the main pole such that the magnetic flux exits through a write pole tip and enters a magnetic medium (disk) adjacent to the ABS. Magnetic flux is used to write a selected number of bits in the magnetic medium and typically returns to the main pole through two pathways including a trailing loop and a leading loop. The trailing loop generally has a trailing shield structure with first and second trailing shield sides at the ABS. The second (PP3) trailing shield arches over the write coils and connects to a top surface of the main pole layer above a back gap magnetic connection. The first trailing shield may have a 19-24 kG magnetic layer called a hot seed layer that adjoins a top surface of the write gap. A good hot seed response is required to reduce stray fields in the side shields and leading shield. The leading shield has a side at the ABS and in a non-double write shield (non-DWS) design is not connected to a return path through the back gap connection to the main pole. Optionally, in a DWS scheme, the leading shield connects to a return path and to the back gap connection to form a leading loop for magnetic flux to return to the main pole. A PMR head which combines the features of a single pole writer and a double layered medium (magnetic disk) has a great advantage over LMR in providing higher write field, better read back signal, and potentially much higher areal density.
For both conventional (CMR) and shingle magnetic recording (SMR), continuous improvement in storage area density is required for a PMR writer. A write head that can deliver or pack higher bits per inch (BPI) and higher tracks per inch (TPI) is essential to the area density improvement. In a typical fully wrapped around shield design for a PMR write head, the main pole and hot seed in the first trailing shield are usually comprised of high a 19-24 kG magnetic material while the leading shield, side shields are made of 10-16 kG magnetic materials, and the remainder of the trailing shield structure including PP3 trailing shield is made of 16-19 kG magnetic material. If writeability can be sustained, a thinner write gap at the main pole trailing (top) surface and a narrower side gap adjoining the main pole sides in the cross-track direction are preferred for better track field gradient (Hy_grad, BPI) and cross-track field gradient (Hy_grad_x, TPI), respectively. To enhance writeability, side shield height reduction is important not only to reduce main pole flux shunting to the side shields, but also to allow more main pole volume closer to the ABS. However, side shield saturation may degrade Hy_grad_x and TPI capability, and is a concern with advanced side shield structures made of 10-16 kG magnetic material with a height of ≦0.15 microns in a side shield region adjacent to the main pole.
Therefore, an improved all wrap around shield design is needed wherein side shield saturation threshold is improved to maintain good writeability with side shield heights of ≦0.15 microns along a side adjacent to the main pole while improving TPI capability to at least 400 Gb/in2 for CMR and at least 500 Gb/in2 for SMR.